Musical Instrument Digital Interface (MIDI) enables the creation polyphonic musical composition with a wide variety of different sounds. This means that multiple tones can be played at the same time using predefined instrument sounds such as piano, guitar, violin and drum. MIDI has been used in mobile terminals to generate ring tones, message alert tones and in games, background music and sound effects. In general, wavetable sound synthesis technology with sampled sounds from real instruments is used for MIDI sound synthesis. The quality of MIDI polyphony for ring tones depends largely on the number of sounds generated expressed as 2n sound polyphony. For example, the sound quality of 64-sound polyphony is superior to that of 16 sound polyphony. In general, generating higher polyphony samples in real-time requires higher processing and computational power. That also means higher costs in manufacturing. In low-end and mid-end mobile terminals, the processing power is generally insufficient to generate high polyphony ring tones and message alert tones.
It is advantageous and desirable to enhance the ring tones and message alert tones in a mobile terminal or in a server where signal processing power is not enough to generate high MIDI polyphony samples in real-time.
Presently, Truetone technology is also used in mobile terminals for producing ring tones or other tones. As it is known in the art, Truetone technology makes it possible to use actual recorded sounds as ring tones and other tones. Truetone technology is based on the Adaptive Multi-rate Wideband (AMR-WB). ABR-WB represents state-of-the-art technology in low bit rate wideband speech coding. Like AMR, it is a multi-rate speech codec. AMR-WB technology uses nine-bit rates between 6.6 and 23.85 kbits/s at 16 kHz sampling rate. The speech processing is performed on 20 ms frames, so each AMR-WB encoded frame represents 320 speech samples. The technology has been optimized for a high-quality natural sound while still keeping the file sizes reasonably small. Small file size makes it possible to deliver the tones over the air making the purchase of Truetone ring tones similar to the purchase of MIDI ring tones. However, Truetone technology that is presently used in a mobile terminal or in a server of a service provider is meant to be a complementary technology to MIDI ring tone generation. It is also possible to use different compressed file formats like MP3, wav, AAC, RealAudio, Vorbis etc for ringing tone.
As shown in exemplary FIG. 1, a Truetone player is used, along with a MIDI player, in a mobile device.